Biogenic oils and fats are usually obtained by mechanical or physio-chemical extraction processes. By these means lipophilic or amphiphilic substances, so-called mucilages, which are dissolvable in oils and fats are liberated also which then leads to contamination of the lipid phase. When this concerns vegetable oils, a variable extent of phospholipids, phenols, dyes such as chlorophylls and carotenoids, glycolipids, free fatty acids, odorants, flavors, and other organic compounds are dissolved in the lipid phase. If this phase is prepared under anhydrous conditions, the resulting lipid phase is clear to slightly cloudy and has a greenish to yellowish or reddish to brownish coloring. The impurities have a negative impact on the shelf life, the optical appearance, and sensory effects if the oil is used for the human consumption. Known from prior art are methods to reduce these impurities or mucilages, respectively, can be achieved. These mucilages are at least in part complexed with other amphiphilic or lipophilic substances by electrostatic forces.
Therefore, aqueous solutions of acids and bases are used under elevated temperature and pressure and a prolonged exposure time, in order to “break-up” these complexes, whereby the amount of separable impurities increases significantly. Particularly phosphorus-containing compounds can be separated by these means, so that residual phosphorus content between 10 and 25 ppm can be achieved, independently from the prior content. If a base was used for degumming, the content of volatile fatty acids, which are also present in lipid phases, can be reduced to values of 0.8 to 0.5 wt % (g/100 g), due to conversion of the acids to the corresponding carboxylates. The color of the thus refined oil is not changed significantly, although the resulting gummy mucus phases have a blackish brown color. From the prior art it is known that by a renewed exposure to an acidic or alkaline solution no relevant changes in the characteristics of the oil can be achieved. There is no aqueous-based refining procedure known from the prior art, by which a further reduction of the residual phosphate content, the coloring of the oil, and the residual content of free fatty acids can be achieved in order to obtain the required levels of purity according industrial standards for their use as food or fuel. Particularly in refining of vegetable oils, various oil impurities must be depleted or removed completely because they cause visual or sensory impairments and decrease storage stability since they may lead to formation of undesirable compounds that even might be toxic. Therefore, additional methods have been developed, by which the according reductions can be achieved. One such method is known under the trademark ZENITH process of Procter & Gamble. In this case, first a degumming process is performed using concentrated phosphoric acid, which is added to the oil and mixed at a temperature between 35° and 50° C. over a period of 30 minutes. Subsequently the aggregated phospholipid mass is separated, and the oil neutralized by base treatment whereby volatile fatty acids are saponified and the so-called soap stock is subsequently removed. Thereafter, the oil is mixed with bleaching earth in order to remove nonhydratable phospholipids and pigments from the oil. The process is completed by deodorization with steam at temperatures of 218° C.-271° C. at 12-4,000 Pa.
Meanwhile, many variations of this method have been published, by which particular adjustments of process conditions are proposed to yield district improvements, e.g., in the reduction of color pigments (e.g., EP 0737238 B1, process for removing chlorophyll dye impurities from plant oils; U.S. Pat. No. 4,443,379, Oil bleaching method and composition for same). Improvements in the reduction of plant dyes were in particular obtained by bleaching earths that have been activated due to acid treatment or by adsorbents such as silica gels, admixed together with phosphoric or sulfuric acid to the oils. However, the by far most appropriate method to achieve a color reduction is the use of phyllosilicates which have a high internal surface area. This requires contacting the oil and the bleaching earth that has been pulverized or ground at an elevated (>60° C.) temperature and under vacuum (<1000 Pa) for at least 30 minutes. By this means color pigments can be depleted, and Lovibond color scale values of R3.0/Y3.9 are achieved as well chlorophyll concentrations are reduced to values of 0.08 ppm.
It was shown that further improvement in the reduction of color pigments can be achieved by activation of bleaching earths with an acid pretreatment. Furthermore, combining silica gels and phosphoric acid or phosphoric acid and sulfuric acid allows the duration of exposure of the adsorbents to be reduced while an equal reduction of the color pigments is achieved; however, the absolute amount of color pigments could not be further reduced. This is because the color pigments are chemically modified, but are not removed from the oil. Thus, it is necessary to perform a further purification step by means of a steam extraction. Application of heat and oxidizing agents can in turn lead to chemical changes of constituents of the oil, such as tocopherols, vitamins, polyphenols and/or cause oxidation products of plant dyes and/or of mucilages and/or generate peroxides of fatty acids. The latter promote generation of further peroxides during the course of storage thereby causing color reversion and of off-flavors, among others.
In the scientific literature it was shown that the organoleptic characteristics and changes in the color of refined oils crucially depend on the process technology used. The decisive condition is the formation of radicals which themselves can cause unwanted sensory or visual effects in addition to their chemical reaction with other organic compounds, which then lead to undesirable effects. The extent of radical formation is thereby essentially determined by the following: 1.) the number of oxidation products that a) were present in the crude oil and were not removed by the refining process, and b) have arisen due to the refining process and 2.) the amount of antioxidant compounds which a) were already present in the crude oil and b) still remained in the refined oil. With the use of methods allowing a better depletion of dyes, especially antioxidants, such as tocopherols, polyphenols or squalene are also reduced to a greater extent.
By oxidative processes, aldehydes, ketones, and free fatty acids among others are formed which accelerate the oxidative processes and are responsible in large part for off-flavors in vegetable oils.
The process steps bleaching and deodorization were found to be essentially responsible for the occurrence of a mismatch between the content of oxidatively modified organic compounds and the content of antioxidant organic compounds in vegetable oils.
Treatment of oils with bleaching earth cause acid-catalyzed oxidation, and, in varying degrees, they deplete compounds having antioxidant properties by adsorption, so the oxidative stability of oil can deteriorate significantly by this process step.
In principle, the same applies for the deodorization process, especially when high steam temperatures (>220° C.) are used and a longer residence time (>15 minutes) for the oil is selected. Thus, the storage stability is influenced by the classical refining methods to varying degrees. Moreover, the storage stability of refined oil is often not superior to that of cold-pressed oil since native oils may contain a greater amount of antioxidants, and processing does not add any further components which promote auto-oxidation. Components which promote auto-oxidation mostly have radical or radical-forming groups. A targeted depletion of these compounds is not possible by methods of the prior art.
Furthermore, there is scientific evidence that formation of secondary oxidation products correlates with the decrease in the sensory quality of the oil. This is because many of the secondary oxidation products themselves, such as aldehydes and ketones, lead to an off-flavor. It could be shown that the concentration of secondary oxidation products, which can be estimated by a reaction with anisidine, predicts both the formation of off-flavors and the extent of color reversion of oils that have been exposed to oxidants and bleaching earths. In this respect, determination of the anisidine value is of practical value, since it correlates with the content of aldehydes (2-alkenals and 2,4-dienals) and ketones.
Further optimization in removal of the color pigments was reported for the combined use of phosphoric and sulfuric acid having a more rapid and stronger bleaching effect. For removal of the acids and the degradation products of the color pigments, a caustic wash stage, which leads to a saponification of acids, is performed. These soaps are difficult to remove from the oils and often result in a loss of product due to additional removal of oil. Furthermore, soaps that remain in the washed oil lead to an unpleasant taste; thus, deodorization by means of steam extraction is still required. Procedures, allowing a depletion of dyes and/or odorants and/or flavors, which are present in vegetable oils, without using bleaching earths and/or deodorization procedures, have yet not been presented.
In vegetable oils, a variety of organic compounds can cause an uncomfortable sensation of the olfactory or gustatory senses. It is often not possible to distinguish whether the sensory perception of a smell or taste is caused by an odorant or a flavoring because the overall sensory impression of a flavor arises due to the merging and interference of nerve impulses that originate from different sensory areas of the nose, mouth, and throat. Therefore, sensory smell and taste attributes overlap.
Organic compounds which lead to an odor or taste perception have a very different origin, corresponding to the different classes of compounds to which they can be assigned. It is believed that there are more than 10,000 different compounds in lipid phases, and especially in vegetable oils, which contribute to sensory effects. The composition differs not only for each type of oil, but also depends on the growth conditions, the extraction process of the oils as well as how clarification and storage is performed, etc. Most flavorings and odorants in the lipid phases are in amounts below the threshold of perception. Removal of these compounds is therefore not necessary.
Most vegetable oils that are used as edible or essential oils, contain one (or more) taste and/or odor component(s) which is (are) considered to be characteristic for the product and which is (are) regarded as a desired positive attribute. For the qualitative assessment of such oils, manifestation and purity of specified sensory characteristics are considered as quality attribute. The presence of other sensory perceptions is interpreted as an off-odor or and off-taste, thus, results in the oil being classified as having inferior quality. Therefore, not all flavorings which are responsible for sensory perception should be removed for producing high-quality oils. Rather, it is the goal of a deodorizing procedure to remove off-flavors. It is therefore necessary, if possible, to remove such disturbing flavorings and odorants from these oils. Lipid phases that are not used for human consumption or for cosmetic applications may also be contain flavorings and odorants which lead to a limitation of the utility of the lipid phase. Examples are fish oils or animal fats or used cooking oils. Since only a few of the organic compounds that are responsible for the various sensory perceptions have been identified, prediction of the perceived sensations through a characterization and quantification of organic compounds present in a lipid phase using chemical analytical methods is not possible.
Methods and procedures to remove flavorings and odorants from lipid phases are known in the art. They are summarized under the term deodorization. The methods are based on the ability of phyllosilicates, which are also used for bleaching lipid phases, to bind organic compounds that are flavorings and odorants. Furthermore, they rely on the oxidizability of some of these organic compounds, e.g., by the use of chlorinated lime, sodium hypochlorite, sodium peroxide, or sodium perborate, and on the removal of these organic compounds by steam extraction. Since depletion of flavorings and odorants by adsorption and oxidants is generally not sufficient, deodorization is generally performed by means of steam extraction. Here, steam temperatures of 230° C. to 280° C. are used for duration of 30 to 60 minutes and a pressure of below 1500 Pa. In this process, steam consumption amounts 0.7 to 1.2 tons per ton of oil.
There are numerous patents on methods for optimizing steam deodorization (EP 0032434 B1 Process for deodorizing edible oil). Volatile organic compounds are very effectively removed with the vapor phase at high temperatures. However, in addition to the intended removal of specific flavorings and odorants, flavorings and odorants which are being characteristic for a vegetable oil are also removed; therefore, the sensory quality of deodorized oil might be inferior to that of the untreated oil.
Process modifications of the steam deodorization process have been introduced, known under the heading “Plant flavor-stable process temperature” (PEFSPT) (U.S. Pat. No. 4,378,317 Process to maintain bland taste in energy efficient oil deodoration system) which aim to selectively keep characteristic flavorings in an oil. In addition, methods have been proposed to address other drawbacks of the steam deodorization, e.g., the oxidation of organic compounds or an undesirable discharge of compounds (e.g., tocopherols) (U.S. Pat. No. 5,315,020 A Method of recovering waste heat from edible oil deodorizer and Improving product stability; AU 2010275318A1 A deodorized edible oil or fat with low level of bound MCPD and process of making using inert gas). Further, treating the lipid phase with high temperature steam produce decomposition products and compounds (polymers, epoxymeres, oxidation products) which are potentially harmful, such as trans fatty acids or monochloro propanediol ester (MCPD), such as 3-monochloropropane-1,2-diol (3-MCPD), as well as phthalates or adipates, for example, diisodecyl phthalate (DIDP). Furthermore, organic compounds are removed, that can improve storage stability of the refined lipid phase and exhibit beneficial health effects, such as tocopherols or carotenoids.
Furthermore, the use of bleaching earths is disadvantageous since process costs significantly increase and there is consumption of resources and waste streams arise, since the process is carried out at elevated temperatures and the bleaching earths are not reusable. Further, there is a relevant loss of oil by unintended discharge while removing bleaching earths from the lipid phase. In addition, antioxidants and phytosterols may be removed from the oil with this step.
Similarly, the vapor extraction (deodorization) leads to a significant increase in process cost and product loss. Therefore, methods which enable a resource-saving optimization of the classical oil refining process and yield biologically improved oil products are still necessary.